The present disclosure relates to investment casting, and more particularly to a casting system for use in investment casting processes.
Gas turbine engines are widely used in aeronautical applications. Improved gas turbine engine efficiency is a prime objective in the aeronautical field. Gas turbine engine components, including but not limited to, airfoils and blade outer air seals (BOAS), that include advanced active element containing alloys are known and provide improved oxidation resistance, improved performance and efficiency and reduced component weight.
Many gas turbine engine components are made in an investment casting process. Investment casting is a commonly used technique for forming metallic components having complex geometries, such as the components of a gas turbine engine. The investment casting process used to create a gas turbine engine component is as follows. A mold is prepared having one or more mold cavities, each having a shape generally corresponding to the component to be cast. A wax pattern of the component is formed by molding wax over a core.
In a shelling process, a shell is formed around one or more such patterns. The wax is removed by melting in an autoclave, for example. The shell is fired to harden the shell such that a mold is formed comprising the shell having one or more part defining compartments that include the core. Molten alloy is then introduced to the mold to cast the component. Upon cooling and solidifying of the alloy, the shell and core are removed, such as by mechanical abrasion, water blasting, and/or leaching, for example.
Investment casting of advanced active element containing alloys requires the use of cores having alternative materials. Traditional cores may include silica, alumina, zircon and/or alumina-silica based compositions. These materials react in varying degrees with the active element containing alloys during casting. As a result, the desired concentration of the active element levels in the alloy are reduced and an undesired reaction layer is produced. Alternate core compositions are known to inherently limit diffusion of active elements, such as high alumina or aluminosilicate compositions, for example. However, these compositions are relatively difficult to process and produce and are cost prohibitive for most applications, such as for cores used in components having advanced cooling geometries.